1. Field of Invention
The present invention relates to a metal terminal suitable for installation on an electrical circuit substrate, and to an electrical circuit substrate having such a terminal installed on it.
2. Description of Related Art
In U.S. Pat. No. 4017143, a metal terminal is shown inserted into a circular installing hole of a circuit substrate so as to bring the metal terminal into contact with a contact region of a printed circuit formed on the inner surface of the installing hole. The metal terminal is of C-shape cross-section, with a slit extending in a direction in which the terminal is inserted into the installing hole to allow the metal terminal to elastically deform in its radial (transverse) direction so that the metal terminal makes elastic contact with the contact region. The outer diameter of the cylindrical metal terminal is axially uniform (i.e. in the metal terminal insertion direction) where it contacts the inner surface of the installing hole. Therefore, in a normally installed state, the metal terminal makes surface-to-surface contact with the contact region. However, if the metal terminal is inclined with respect to the axis of the installing hole, the outer surface of the metal terminal separates from the inner surface of the installing hole and makes point-contact with the edges of the substrate at the openings of the installing hole. Therefore, there may be a defective contact between the metal terminal and the contact region on the inner surface of the installing hole.
It is an object of the present invention to provide a metal terminal capable of maintaining the intended electrical connection, even if the metal terminal is inclined with respect to the axis of an installing hole.
According to the invention, there is provided a metal terminal for insertion into a circular contact hole of an electrical circuit substrate and for making electrical contact with an inner surface of the contact hole. The metal terminal has an insertion portion having a resiliently deformable outer wall which defines a central cavity with a slit that extends along the outer wall in the insertion direction of the terminal and allows the terminal to contract in the transverse direction. Part of the insertion portion is tapered and narrows smoothly in the insertion direction.
When the terminal is inserted into the contact hole, the outer peripheral surface of the tapered part at the widest portion thereof bears resiliently on the inner surface of the contact hole along a linear contact region. When this occurs, the tapered part gradually contracts elastically as its diameter gradually decreases. Therefore, the metal terminal has a low insertion resistance, making it easy to use. Further, if the metal terminal becomes inclined with respect to the axis of the contact hole, the outer peripheral surface of the tapered part can maintain a circumferential linear contact with the inner surface of the contact hole.
It is preferable that the outer peripheral surface of the tapered part is outwardly convex at its widest portion. Therefore, if the metal terminal is inclined with respect to the axis of the contact hole, there is a reduced risk of the outer peripheral surface of the tapered part damaging the contact region formed on the inner surface of the contact hole.
Another aspect of the present invention provides an electrical circuit substrate having a contact hole, into which a metal terminal, as described above, is inserted. Typically the substrate has electrical circuit elements on at least one of its surfaces, and the terminal makes electrical contact with such a circuit element via a conductive layer in the contact hole.